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Genetic variation in drought hardiness of coastal Douglas-fir seedlings from British Columbia

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Genetic variation in drought hardiness traits and their genetic correlations with growth potential and recovery traits were investigated in 39 full-sib families of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) from southwestern British Columbia. Seedlings of these families were grown in raised nursery beds and subjected to three moisture regimes each in the second (well-watered or control, mild, and moderate drought) and third (control, severe drought, and recovery from second-year moderate drought) seasons. Traits assessed included drought hardiness (foliage damage, cavitation of xylem tracheids, xylem hydraulic conductivity, and height and diameter growth increment) in the drought treatments, growth potential (total height and diameter) in the control treatment, and height and diameter growth increments in the recovery treatment. Xylem cavitation in the growth ring produced in a particular year was nearly three times greater under the moderate drought and four times greater under the severe drought than in the control treatment. Xylem hydraulic conductivity of seedlings in the severe drought treatment was 40% lower than conductivity of seedlings under the control treatment. Mean foliage damage in seedlings subjected to severe drought (third season) was much greater (33%) than in seedlings subjected to mild or moderate drought (second season). Families differed significantly in most drought hardiness traits, with individual tree heritabilities averaging 0.19. Thus, much potential exists for identifying drought-hardy families at the seedling stage and using this information for deployment or breeding purposes. In addition, most hardiness traits were strongly intercorrelated (genetic correlations often exceeded |0.80|) indicating that these traits are controlled largely by the same set of genes and that selection for hardiness based on one trait will increase hardiness as reflected in the other traits as well. Genetic correlations were only moderate (0.49) between hardiness traits measured in different years, perhaps due to the large difference in severity of the drought applied in the two seasons. Although injury to seedlings, as reflected in foliage damage and xylem cavitation, was relatively low under the moderate drought of the second season, it did result in reduced growth increment the following (recovery) year. Growth potential under favorable moisture regimes was nearly uncorrelated with drought hardiness, suggesting that drought hardiness could be improved in this southwestern British Columbia breeding population without negatively impacting growth potential in favorable moisture conditions.

Les auteurs ont étudié la variabilité génétique des caractères de résistance à la sécheresse et leurs corrélations génétiques avec le potentiel de croissance et les caractères de rétablissement chez 39 descendances biparentales de douglas de Menzies typique (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) provenant du Sud-Ouest de la Colombie-Britannique. Les semis de ces familles ont été cultivés dans des planches et soumis à trois régimes hydriques au cours de la deuxième (irrigation adéquate ou témoin, sécheresse légère et sécheresse modérée) et de la troisième saison de croissance (témoin, sécheresse sévère et rétablissement après la sécheresse modérée de la seconde saison). Les caractères étudiés comprenaient la résistance à la sécheresse (les dommages foliaires, la cavitation dans les trachéides du xylème, la conductivité hydraulique du xylème ainsi que la croissance annuelle en hauteur et en diamètre) pour les traitements de sécheresse, le potentiel de croissance (la hauteur totale et le diamètre) pour le traitement témoin, ainsi que la croissance annuelle en hauteur et en diamètre pour le traitement de rétablissement. La cavitation dans les éléments de xylème du cerne annuel d'une année donnée était presque trois fois plus élevée pour le traitement de sécheresse modérée et quatre fois plus élevée pour le traitement de sécheresse sévère que pour le traitement témoin. La conductivité hydraulique du xylème des semis soumis aux conditions de sécheresse sévère était 40 % plus faible que celle des semis dans le traitement témoin. Les dommages foliaires moyens chez les semis soumis à la sécheresse sévère (troisième saison) étaient beaucoup plus importants (33 %) que

Document Type: Research Article

Publication date: October 1, 2002

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